replace-elements-with-greatest-element-on-right-side.py

# Given an array arr, replace every element in that array with the greatest element among the elements to its right, and replace the last element with -1.
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# After doing so, return the array.
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#  
# Example 1:
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# Input: arr = [17,18,5,4,6,1]
# Output: [18,6,6,6,1,-1]
# Explanation: 
# - index 0 --> the greatest element to the right of index 0 is index 1 (18).
# - index 1 --> the greatest element to the right of index 1 is index 4 (6).
# - index 2 --> the greatest element to the right of index 2 is index 4 (6).
# - index 3 --> the greatest element to the right of index 3 is index 4 (6).
# - index 4 --> the greatest element to the right of index 4 is index 5 (1).
# - index 5 --> there are no elements to the right of index 5, so we put -1.
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# Example 2:
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# Input: arr = [400]
# Output: [-1]
# Explanation: There are no elements to the right of index 0.
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#
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# Constraints:
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# 	1 <= arr.length <= 104
# 	1 <= arr[i] <= 105
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#


class Solution:
    def replaceElements(self, arr: List[int]) -> List[int]:
        def maximum(a, b):
            return a if a >= b else b
        largest = arr[-1]
        for i in range(len(arr) - 2, -1, -1):
            current = arr[i]
            arr[i] = largest
            largest = maximum(current, largest)
        arr[-1] = -1
        return arr